The corresponding example of 6-point metric space was constructed by Sergei Ivanov, see [1]}.
Theorem , provides a source for such examples — any 6-point metric space that satisfy all 5-tree comparisons, but does not satisfy 2(2)-tree comparison provides an example.
This class of examples includes the example of Sergei Ivanov — in the notations of [1]} it does not satisfies the comparison for the tree \(y/az(q/xb)\) .
